The Most Caffeinated Beverages

Energy drinks are now a $12.5 billion industry – and how they impact the health of the millions who drink them regularly is still fairly unknown. "When people pick up an energy drink, more likely than not they don't have a really good sense of what it is they're drinking," says Kathleen E. Miller, a senior research scientist at the University at Buffalo's Research Institute on Addictions. Thanks to a few extreme cases, like the 14-year-old who died from too much caffeine after two energy drinks. Investigators found she had a preexisting heart condition, but concerns about caffeine are still growing.

Last year, Kathleen Miller was one of fifteen signatories on a letter sent to Food and Drug Administration Commissioner, Margaret Hamburg, that voiced concerns about the safety of energy drinks. Miller says these drinks are of particular concern because they are not required to disclose their caffeine contents. Many of them are classified as dietary supplements, which limits the FDA's power over them. Energy drinks also often contain secondary ingredients, like guarana, gingko biloba, and ginseng, which may alter caffeine's effects.

Moderate caffeine intake has been linked to enhanced alertness, focus, endurance, and even memory gains but too much can cause jitters, nausea, insomnia, and heart palpitations. Reach over 1,000 milligrams of caffeine in one day (about 10 cups of coffee) and you risk caffeine toxicity, symptoms of which can include seizures, hallucinations, and stroke. Here's a look at a number of common energy drinks and how to measure when you hit 500 mg – the point where caffeine intake starts to get dangerous